Substation circuits



I 1,618, 01 Feb. 22,1927. A. [News 2 SUBSTATION CIRCUITS Fil'd April 25. 1925 Juklriberj Lime INVENTOR M l y 0 ATTORNEY Patented Feb. 22, 1927. v

UNITED STATES PATENT OFFICE.

ALFRED H. INGLIS, ORANGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK.

SUBSTATION CIRCUITS.

Application filed April 25, 1925. Serial No. 25,940.

This invention relates toigtelephone substation circuits.

The principal object of the invention is the satisfactory transmission of speech which is abnormally low, for instance, the mere whisper of one Who has lost the use of his vocal cords. Other objects and advantages of the circuit arrangement will be made clear by the following detailed description.

Applicant combines with certain subscriber station apparatus, well known in the art, amplifying means for compensating for the low voice level and suitable means for 1 switching the amplifier in and out of the subscribers circuit.

The detailed descri tion of the circuits is to be read with re erence to the accompanying drawing, which shows diagram- 2 matically the circuit arrangement.

lVith reference to the details of the drawing, the receiver 1, the switchhook 2, the contacts associated therewith, the ringer 3, the condenser 4, and the induction coil 5 2 are apparatus usually'found in substation sets. The transmitter 6 may be any transmitter which is of sufficiently high quality for use in transmitting speech of the low level of a whisper and at the same time suitable for service in the ordinary telephone substation set.

a The amplifying means shown in the drawing is a two-stage amplifier using vacuum tubes and comprises the input transformer 7, the output transformer 8, the thermionic vacuum tubes 9 and 10, and the inter-stage transformer 11. The battery 12 serves as a source of current for theplates of the tubes and the battery 13 is the fila- 4 ment current source. The grid biasis obtained from the potential drop in the filaments.

Suitable switching means are provided whereby the amplifying means may be connected 1nto or cut out of the subscribers circuit. When the speech to be transmitted is normal, of course, the amplifier is not used, and the key lever 14 remains in the position indicated in the drawing, contact being made between points 18. and 19 and 20 and 21, which connections complete the circuits of the substation set without including the amplifier.

If the speech to be transmitted is abnormally low, the lever 14 is thrown down, contact between points 18 and 19 and 20 and 21 is broken, and contact is made between points 15 and 16, 17 and 18, 21 and 22, and

r 21 and 24. The contact made between points 17, and 18 and 21 and 22 connects the primary winding of the input transformer 7 across the transmitter circuit at and 26. The contact made between points 15 and 16 connects one terminal of the secondary winding of the output transformer 8 to thepoint 27 on one side of the subscriber line, and the contact made between points 23 and 24 connects the other terminal of the same winding to the other side of'the subscriber line through point 28 and the switchhook.

The filament current of the amplifier is controlled by a relay, shown in the drawing, with electromagnet 29 and armature 30. This relay, as clearly appears from the circuit diagram, is operated by the switchhook 2 and makes and breaks the filament circuit at 31.

What is claimed is:

1. A telephone substation system including a transmitter, a receiver, a line circuit, a switchhook controlling the connection of said transmitter and receiver with said line circuit, a vacuum tube current amplifying device, a relay controlling the filament circuit of said amplifying device, and a single switching means for connecting the input of said amplifying device to the transmitter points 25 and the output thereof to the line circuit and for connecting said relay to the line circuit through the switchhook.

2. A telephone substation system including a transmitter, a receiver, a line circuit,

a switchhook controlling the connection of I said transmitter and receiver with said line circuit, a vacuum tube current amplifying device, a relay controlling the filament circuit of said amplifying device, and a twoposition switch, said switch in the first posicircuit, and the relay to said circuit through tion connecting.the-transmitter to the line the switchhook. circuit through the switchhook and discon- In testimony whereof, I have signed my 1 necting the relay from said circuit, and inname to'this specification this'23rd day of 5 the second position connecting the input of April, 1925.

the current amplifying deviceto the'tra ns 7 mitter, the output of said device to the line ALFRED H. INGLIS. 

